The Dental Biology Unit is directed by Dr. Songtao Shi and currently includes Drs. Masako Miura, Byoung-Moo Seo and Takeo Tsutsui. Because the unit as been independent for only several months, the close collaboration with Dr. Shi!'s previous Section (Skeletal Biology Section at CSDB led by Dr. Pamela G. Robey) is obvious. Our research is focused on isolation and characterization of dental/craniofacial associated stem cells including stem cells from Dental Pulp Stem Cells (DPSCs) and Human Exfoliated Deciduous teeth (SHED). Our previous studies identified that adult human dental pulp contained a clonogenic and rapidly proliferative population of cells, named dental pulp stem cells (DPSCs). DPSCs were then compared to human bone marrow stromal stem cells (BMSSCs), known precursors of osteoblasts. Although they share a similar immunophenotype in vitro, functional studies showed that DPSCs produced only sporadic, but densely calcified nodules. When DPSCs were transplanted into immunocompromised mice, they generated a dentin-like structure lined with human odontoblast-like cells that surrounded a pulp-like interstitial tissue. In contrast, BMSSCs formed lamellar bone containing osteocytes and surface lining osteoblasts, surrounding a fibrous vascular tissue with active hematopoiesis and adipocytes. This study was the first to isolate post-natal DPSCs that have the ability to form a dentin/pulp-like complex. Furthermore, we characterized the self-renewal capability, multi-lineage differentiation capacity, and clonogenic efficiency of DSPCs. Stromal-like cells were re-established in culture from primary DPSC transplants and re-transplanted into immunocompromised mice to generate a dentin-pulp-like tissue, demonstrating their self-renewal capability. DPSCs were also found to be capable of differentiating into adipocytes and neural-like cells. The odontogenic potential of twelve individual single-colony derived DPSC strains was determined. Two thirds of the single-colony derived DPSC strains generated abundant ectopic dentin in vivo, while only a limited amount of dentin was detected in the remaining one third. These results indicate that single-colony derived DPSC strains differ from each other with respect to their rate of odontogenesis. To isolate high quality human postnatal stem cells from accessible resources is an important goal for stem cell research. We found that exfoliated human deciduous teeth contain multipotent stem cells (Stem cells from Human Exfoliated Deciduous tooth, SHED). SHED were identified to be a population of highly proliferative clonogenic cells capable of differentiating into a variety of cell types including neural cells, adipocytes, as well as odontoblasts. Upon in vivo transplantation, SHED were found to be able to induce a significant amount of bone formation, generate dentin, and survive in mouse brain along with expression of neural markers. Our studies demonstrated that a naturally exfoliated human organ contains a novel population of stem cells that are completely different from previously identified stem cells. SHED are not only derived from a very accessible tissue resource, but are also capable of providing enough cells for potential clinical application. Thus, exfoliated teeth may be an unexpected unique resource for stem cell therapies including autologous stem cell transplantation and tissue engineering. Recently, a great deal of effort has been done in CSDB to identify the potential niche of mesenchymal stem cells, which will be critical for understanding their functional characteristics. We found that DPSCs reside in the microvasculature of dental pulp and they were isolated by immunoselection using the antibody, STRO-1, that recognizes an antigen on stromal elements and perivascular cells in dental pulp tissue. Freshly isolated STRO-1 positive DPSCs were found to lack expression of von Willebrand Factor (an endothelial cell marker) but were positive for alpha-smooth muscle actin (smooth muscle cell marker) and MUC-18 (endothelial cell marker). Furthermore, the majority of DPSCs expressed the pericyte marker, 3G5. The finding that DPSCs display phenotypes consistent with different perivascular cell populations may have further implications in understanding the factors that regulate the formation of mineralized matrices and other associated connective tissues.